Decommissioning Insight 2016 - Oil & Gas UK

DECOMMISSIONING INSIGHT REPORT 2016

5.4 Subsea Infrastructure Decommissioning Mattresses are concrete structures usually used to protect or support subsea pipelines. Mattress decommissioning typically involves recovery from the seabed. This is a diver and vessel-intensive operation, with duration of the work dependent on the mattress age and condition. In some cases where the mattresses are badly degraded, regulatory approval may be sought to decommission mattresses in situ .

Other subsea infrastructure includes manifolds, Christmas trees, risers, spools, jumpers, anchors and subsea isolation valves, which are removed as part of the decommissioning programme.

• Just under 12,000 mattresses are forecast to be decommissioned across the UK and Norwegian Continental Shelves from 2016 to 2025.

• Sixty per cent of this activity (see table opposite) is concentrated in the central and northern North Sea and �est of Shetland; 38 per cent in the southern North Sea and Irish Sea; and the remaining two per cent on the Norwegian Continental Shelf.

• Just over 64,400 tonnes of other subsea infrastructure will be removed from the UK and Norwegian Continental Shelves from 2016 to 2025, compared with 86,000 tonnes forecast a year ago.

• The decrease in subsea infrastructure removal compared with last year is due to subsea infrastructure removal falling outside the survey timeframe for many of the projects included.

• Ninety-one per cent of this activity is concentrated in the central and northern North Sea and west of Shetland, six per cent is in the southern North Sea and Irish Sea, and three per cent on the Norwegian Continental Shelf.

• All of the mattress and other subsea infrastructure decommissioning activity on the Norwegian Continental Shelf is concentrated in the Norwegian North Sea.

• The large amount of mattress and other subsea infrastructure activity in the central and northern North Sea and �est of Shetland is due to the scale and types of projects in these regions. There are 13 fields serviced by FPSOs plus a number of projects with multiple subsea tie-backs.

• The relatively low forecast on the Norwegian Continental Shelf is due to there being fewer decommissioning projects in this region and activity for many projects lies outside the survey timeframe.

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